The cameras picked up images of the whole in Walkers window and wall beside his head. That can't be faked.
Would you please post the photos? I believe you'll find that Walker would have to have been about 4 feet tall if the bullet was anywhere near his head. Personally, I doubt that Walker was even in the room when the bullet zipped through the window..... Walker and Lee Oswald would have been the only two who who would know.
P.S. If you'll post the DPD photos of the "crime scene".... I may be able to show you some startling evidence.